Congestive heart failure is a major problem in today—over 5 million patients in the U.S. and probably even more in the EU are afflicted. There is no effective medication to improve the strength of heart contraction and to date there has been little advancement toward solving this problem on a mass scale. Attempts should be directed to a simple, proven and minimally invasive system to help these patients.
Aortic counterpulsation is a well-established form of assistance for a failing heart. In one type of counterpulsation procedure, as the heart ejects blood in systole, blood is removed from the aorta thus relieving the work of the heart in ejecting blood. As the heart relaxes in diastole, the removed blood is pumped back into the aorta increasing the blood pressure and flow to the organs. This assists the heart for two reasons. First, the work on the heart is reduced because blood is withdrawn from the aorta as the heart is working (cardiac unloading). Second, the heart is unusual among organs in that most of its perfusion occurs during diastole so that higher pressures during diastole cause a major improvement to the flow of blood in the heart. Improved perfusion and oxygenation of the heart and reduced work performed by the heart typically result in improved performance of the heart and improved circulation for the entire body. Many patients have been saved from certain death by application of this concept. Failing hearts and vital organs such as kidneys are frequently resuscitated by this method.
Most commonly, counterpulsation is achieved with a balloon inside the aorta rather than actually removing blood and returning blood to the aorta. This device is known as the intraaortic balloon pump. In practice a patient receives a balloon mounted (usually about 40 ml in size) on a catheter (1-2 m long). The catheter is introduced into the patient via a groin artery. The balloon resides in the descending aorta (beyond the take-off of the vessels to the head and neck). The balloon is deflated in systole to help the heart eject (rather than remove the blood) and inflated in diastole (rather than return the blood). The balloon is inflated and deflated by gas (usually helium) which is shuttled in and out of the catheter. The passage of the gas is driven and controlled by a console which times or coordinates the movement of gas with the patient's EKG to ensure that the optimal timing of the inflation and deflation occurs to ensure maximal improvement in cardiac performance results.
The intraaortic balloon pump has a number of major drawbacks. First, it is almost always inserted by a puncture in a major groin artery. The patient must remain supine in bed. Movement is extremely limited as movement on the catheter may cause bleeding from the artery which has been punctured. Patients often deteriorate while supine as muscles weaken from inactivity and the risk of pneumonia and leg clots increases.
Infection is also a major concern. The catheter travels out of the groin artery of the patient. Any catheter tracking into the body tends to become colonized with bacteria. Over time the bacteria travel up the catheter and into the blood stream. As the groin area is plentiful with bacteria, this area is particularly ripe for the origin of infection.
Another concern is that of limb ischemia. The catheter may be close to the size of the patients groin artery and may occlude the flow of blood to the leg and risking the loss of that limb. Even when the groin arteries are large, over time clotting tends to occur around the catheter and flow becomes reduced to the limb beyond the entry site. After a number of days there is an increasing risk of leg ischemia and leg loss.
In clinical practice, an intraaortic balloon pump usually remains in place just a day or two. If it is left more than about a week, the doctors become extremely concerned that a serious complication will occur and typically remove the balloon.
Many patients have chronically weakened hearts that require long-term support. Despite the fact that counterpulsation is extremely helpful to these patients, there has been no way to apply this technology practically for a long period of time (i.e., months or years). It would be very valuable for patients to have a system that provides counterpulsation but does not carry the risks of the intraaortic balloon pump.
Furthermore, these patients are very ill and cannot tolerate major procedures. An attempt has been described to perform long-term counterpulsation by opening the patient's chest and then sewing a balloon pouch inside the aorta. This pouch is then attached to a drive line. Initial studies suggest that this does indeed provide considerable long term help to a failing heart. However, it is unlikely that this procedure could ever be used on a large scale as it is so invasive. In another approach, the counterpulsation pouch has been sewn to the thoracic or abdominal aorta. However, this requires a major procedure—a thoracotomy or a laparotomy to gain entry to the chest or abdominal cavity.
Blood pumps have also been used to assist the failing heart. In general, blood is taken from the left atrium or left ventricle and then pumped into the aorta. This form of cardiac assist is extremely effective. However, there are a number of problems that have not been satisfactorily solved and this technology is not yet widely used in heart failure. The first problem is that insertion of these devices requires a major procedure for connection to the heart and the aorta. The pumps have blood contacting surfaces, particularly bearings, and these are prone to clotting. Clots may either break loose and embolize (migrate) to the body causing strokes or other organ problems or may stay in place and enlarge to the point that they cause the device to malfunction. The systems also contain valves which regulate the direction of flow in the system. These valves, in combination with stasis points within the system may also contribute to clotting. Another major problem with these devices is that they require major regulation. It is never clear how much blood should be pumped. If too little is pumped, the patient suffers from insufficient circulation. If the pump is set too high, the heart can be sucked flat and then drawn into the pump with serious consequences to the heart. Patients in heart failure have considerable variation over time in the fluid volume of their hearts and the flow rates in the circulation. If the pump does not precisely respond to these variations, failure may occur.
Counterpulsation eliminates many of the problems with blood pumping. There is no necessity for pump bearing-to-blood contact as the blood can fill and empty from a blood sac insulated from the driving pump or device. No valves are necessary. Stasis is minimal as the blood fills and empties completely from the blood sac on each cardiac cycle. Perhaps most important is that the regulation of this device is simple. The system is not connected directly to the heart. Thus it can fill and empty each cycle without the need to adjust the volume that is pumped by the system.
In summary, aortic counterpulsation is a proven form of heart assist in acute and chronic heart failure. Unfortunately, no chronic form has been developed that can be provided to the patient in a minor procedure, allows mobility and reduces the risk of long term infection. Such a system would be very useful to the millions of patients suffering from congestive heart failure.